Biosynthesis of Fatty Acids

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Questions and Answers

What is the primary location of fatty acid synthesis?

Cytosol

Adipose tissue and liver (correct)

Erythrocytes

Mitochondria

What is the source of acetyl CoA in fatty acid synthesis?

Oxidation of fatty acids

Oxidation of pyruvate

Degradation of ketone bodies

All of the above (correct)

Why is the coenzyme A portion of acetyl CoA not transported to the cytosol?

Because it is too large to cross the mitochondrial membrane

Because it cannot cross the mitochondrial membrane (correct)

Because it is not soluble in water

Because it is negatively charged

What is the purpose of citrate synthase in fatty acid synthesis?

To condense oxaloacetate and acetyl CoA Signup and view all the answers

Why can't the brain and erythrocytes use fatty acids as a source of fuel?

Because they require a constant supply of glucose Signup and view all the answers

What is the energy source for the carbon-carbon condensations in fatty acid synthesis?

Carboxylation and decarboxylation of acetyl groups Signup and view all the answers

What is the rate-limiting and regulated step in fatty acid synthesis?

Carboxylation of acetyl CoA Signup and view all the answers

What is required for the carboxylation of acetyl CoA to form malonyl CoA?

Biotin, ATP, and bicarbonate Signup and view all the answers

What is the effect of citrate on acetyl CoA carboxylase?

Allosteric activation Signup and view all the answers

What is the role of malonyl-CoA in regulating acetyl CoA carboxylase?

Allosteric inactivation Signup and view all the answers

What is the effect of epinephrine on acetyl CoA carboxylase?

Phosphorylation and inactivation Signup and view all the answers

What is the result of a prolonged consumption of a high-calorie, high-carbohydrate diet on acetyl CoA carboxylase synthesis?

Increased synthesis Signup and view all the answers

What is the enzyme responsible for the elongation of the fatty acid chain in 2-carbon increments?

Fatty acid synthase Signup and view all the answers

What is the function of acyl carrier protein (ACP) in fatty acid synthase?

Covalently binds to Pantothenic acid and carries acetyl and acyl units Signup and view all the answers

What is the product of the carboxylation of acetyl CoA?

Malonyl-CoA Signup and view all the answers

What is the subcellular location of the first step of fatty acid biosynthesis?

Mitochondria Signup and view all the answers

Study Notes

Fatty Acid Synthesis (Lipogenesis)

Excess carbohydrates and proteins can be converted to fatty acids and stored as triglycerols.
Fatty acid synthesis occurs primarily in the liver and adipose tissue.

Stage 1: Mitochondria

Acetyl CoA is produced from:
- Oxidation of pyruvate
- Degradation of fatty acids
- Degradation of ketone bodies
Acetyl CoA is transferred from the mitochondrial matrix to the cytosol in the form of citrate.

Stage 2: Cytosol

Citrate is cleaved by ATP-citrate lyase to produce cytosolic acetyl CoA and oxaloacetate.
Carboxylation of acetyl CoA to form malonyl CoA requires:
- Acetyl CoA carboxylase
- Biotin
- ATP
- Bicarbonate (HCO3-)
Acetyl CoA carboxylase is a multienzyme protein consisting of 3 identical functional subunits.

Regulation of Acetyl CoA Carboxylase

Short-term regulation:
- Citrate: allosteric activation
- Palmitoyl-CoA: allosteric inactivation (feedback inhibition)
- Malonyl-CoA: allosteric inactivation
- Reversible phosphorylation: regulated by cAMP-dependent protein kinase
Long-term regulation:
- High-calorie, high-carbohydrate diets: increase acetyl CoA carboxylase synthesis and fatty acid synthesis
- Low-calorie diet or fasting state: decrease acetyl CoA carboxylase synthesis and fatty acid synthesis

Fatty Acid Synthesis (Continued)

Step 3: Elongation of the fatty acid chain (in 2-carbon increments) by fatty acid synthase.
Fatty acid synthase (FAS):
- Dimeric enzyme
- Each monomer composed of:
  - 7 different enzymatic activities
  - Acyl carrier protein (ACP): covalently binds to pantothenic acid, carrying acetyl and acyl units on its terminal thiol (-SH) group.

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Description

Learn about the process of fatty acid synthesis, where excess carbohydrates and proteins are converted to fatty acids and stored as triglycerols, primarily in the liver and adipose tissue.